From European Published Patent Application No. 0 477 400, a system for an adaptive, mechanical tolerance compensation acting in the lift direction is known for a travel transducer of a piezoelectric actuator for a fuel injector. In the process, the actuator lift is transmitted via an hydraulic chamber. The hydraulic chamber has a defined leak with a defined leakage rate. The actuator lift is introduced into the hydraulic chamber via a transmitter piston and transmitted to an element to be driven via a receiver piston. This element is, for example, a valve needle of a fuel injector.
Guided in the master cylinder is a slave piston, which also seals the master cylinder and thereby forms the hydraulic chamber. Arranged in the hydraulic chamber is a spring that presses apart the master cylinder and the slave piston. When the actuator transmits a lift movement to the master cylinder, this lift movement is transmitted to the slave piston by the pressure of an hydraulic fluid in the hydraulic chamber since the hydraulic fluid in the hydraulic chamber is unable to be compressed and only a small fraction of the hydraulic fluid is able to escape through the annular gap during the short duration of a lift. In the rest phase, when the actuator exerts no compressive force on the master cylinder, the spring pushes the slave piston out of the cylinder and, due to the generated vacuum pressure, the hydraulic fluid penetrates the hydraulic chamber and replenishes it via the annular gap. In this way, the hydraulic coupler automatically adapts to linear deformations and pressure-related expansions of a fuel injector. The hydraulic medium is sealed via sealing rings.
Also known from the related art are fuel injectors that seal the hydraulic medium with seals in the shape of a corrugated tube or convoluted bellows. Disadvantageous in this known related art is that the restoring force is generated solely by the spring. Changes in the behavior of the spring, for instance due to ageing, therefore have a greater effect on the restoring force and thus on the coupler's behavior. Furthermore, the size of the spring is larger.